As shown in FIGS. 1-3, a gas valve seat of the prior art consists of a switch valve body 2 which is provided therein with a control chamber 24 which is in turn provided therein with a valve body 27, and two plug rings 25 and 26. The valve body 27 and the two plug rings 25 and 26 are forced by a fitting tube 3 to locate hermetically in the control chamber 24.
Such a prior art gas valve seat as described above is defective in design in that the valve body 27 is often not in an intimate contact with the plug rings 25 and 26, thereby resulting in the formation of small gaps 28, as shown in FIGS. 2 and 3. The gaps 28 are often responsible for a gas leak. In addition, the formation of the gaps 28 can result from the wear of the valve body 27 as well as the plug rings 25 and 26. Moreover, the wear of the valve body 27 or the plug rings 25 and 26 can be compounded under the circumstance that the fitting tube 3 is not securely fastened with the switch valve body 2, thereby intensifying the wear of the valve body 27 or the plug rings 25 and 26 at the time when the pilot knob 11 is turned.